Ever since he strummed acoustic on the San Diego coffeehouse circuit nearly two decades ago, double-Grammy-winning folk-popper Jason Mraz thought he learned everything he could about entertaining an audience — like how to tweak the subtly tropical hooks in a worldwide smash like “I’m Yours” into a joyful sing-along.

But that was before his eye-opening, 14-week run on Broadway earlier this year, playing Dr. Jim Pomatter in Sara Bareilles’ musical version of the 2007 film “Waitress,” at her personal request. She starred opposite him for much of that time.

Mraz, who plays Berkeley this week, touting his new sixth record “Know.” (carefully crafted as a feel-good panacea that skirts Trump references) first noticed the Xs dotting the stage when he arrived at New York’s Brooks Atkinson Theatre last fall. Each represented a directorial mark he had to memorize, he learned. “Or places to get to, places to arrive at in your dialogue that can then evolve into a song that the band is waiting to begin; it was much harder than your typical concert rehearsal, just learning what I’m supposed to show up and do.”

His “Waitress” debut last Nov. 3 was a disaster. “I forgot to go on,” he sheepishly admits. “There were so many things I had to remember, so I’m just sitting in the wings, watching this scene, when I notice that I’m supposed to be in that scene, so I had to run onstage, which got a big laugh because my character is quite clumsy.”

He’s glad the gaffe happened Day One. It kept him prompt, prepared, and precise for the rest of his run. He learned trade tricks, too. “If a cellphone rings in the audience, you can say, ‘I told you to hold all my calls,’” he says.

At 18, Mraz had visited New York to attend a music theater school, but quickly tired of the thespian life. Instead, he perfected his lazy, Brazilian-flowery acoustic sound and defined on his 2002 bow, “Waiting For My Rocket to Come.” He’d been friends with Bareilles for a decade, and sung two tunes on her 2015 non-cast recording “What’s Inside: Songs From Waitress.”

“Then she called again and asked if I would consider singing those songs in the production,” he says. “I never saw it coming, never had a clue.”

Until then, the fedora-sporting artist was content with his “Family Guy” cameo, where he — having been identified by Peter Griffin — drolly responds, ‘I’m not Jason Mraz. I’m just a guy in a hat.’ He sighs. “I’m still just a guy in a hat, and some days I do feel like a parody of myself,” he says. “But it’s not a bad hat to wear, and it’s not a bad gig. And I’m really grateful.”